Alien crosstalk suppression with enhanced patch cord

ABSTRACT

Systems and methods for decreasing alien crosstalk use enhanced patch cords for introducing additional attenuation. The enhanced patch cords are preferably shielded to reduce alien crosstalk down their lengths and also attenuate signals passing therethrough to a greater extent than standard communication patch cords. The interaction of two enhanced patch cords results in two suppression steps for alien crosstalk and only one suppression step for intended signal passing through a communication cable.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/539,947, filed Jul. 2, 2012; which is a continuation of U.S. patentapplication Ser. No. 12/788,891, filed May 27, 2010, which issued asU.S. Pat. No. 8,217,268 on Jul. 10, 2012; which is a continuation ofU.S. patent application Ser. No. 11/468,848, filed Aug. 31, 2006, whichissued as U.S. Pat. No. 7,728,228 on Jun. 1, 2010; which is acontinuation of U.S. patent application Ser. No. 10/887,718 filed Jul.9, 2004, which issued as U.S. Pat. No. 7,109,424 on Sep. 19, 2006; whichclaims the benefit of U.S. Provisional Patent Application Ser. No.60/486,683, entitled “Alien Crosstalk Suppression with Enhanced PatchCord Design,” filed on Jul. 11, 2003; U.S. Provisional PatentApplication Ser. No. 60/488,566, entitled “Alien Crosstalk SuppressionWith Enhanced Patch Cord,” filed on Jul. 18, 2003; and U.S. ProvisionalPatent Application Ser. No. 60/565,464, entitled “Alien CrosstalkSuppression with Enhanced Patch Cord,” filed on Apr. 26, 2004. Theseprovisional applications are further incorporated herein in theirentireties.

FIELD OF THE INVENTION

The present invention relates generally to communications systems andmore specifically relates to systems and methods for suppressing aliencrosstalk in communications.

BACKGROUND OF THE INVENTION

Suppression of crosstalk in communication systems is an increasinglyimportant practice for improving systems' reliability and the quality ofcommunication. As the bandwidth of a communication systems increases, sodoes the importance of reducing or eliminating signal crosstalk.

In wired communication systems, crosstalk is caused by electromagneticinterference within a communication cable or between multiple cables.Crosstalk resulting from interaction between cables is known as aliencrosstalk.

While crosstalk resulting from signals running within a single cableinterfering with signals within the same cable can be managed usingelectronic crosstalk reduction methods, alien crosstalk poses additionalproblems because the qualities of the interfering or disturbingsignal(s) are not known. Alien crosstalk has proven problematic inimplementations such as 10 Gbps Ethernet communication over an installedbase of Cat 6 or Cat 5e cable. In such cables, alien crosstalk cansignificantly hamper communication performance. Specially-designedcabling could be used to decrease alien crosstalk, but replacingexisting cabling with newly-designed cabling entails significantexpense.

Thus, there exists a need for alien crosstalk suppression methods andsystems that may be used with installed cable.

SUMMARY OF THE INVENTION

According to one embodiment of the present invention, an improved patchcord having increased attenuation improves performance of an installedcabling system.

According to another embodiment of the present invention, aliencrosstalk between communication cables is decreased by a method of usingattenuating patch cables connected to the communication cables.

According to another embodiment of the present invention, cablingsystems employ an improved patch cord to decrease alien crosstalkbetween communication cables.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a communication system according to oneembodiment of the present invention;

FIG. 2 is a schematic view of a cabling installation with improved patchcords for providing alien crosstalk suppression;

FIG. 3 is a graph showing the increased signal-to-noise ratio in acommunication system using an enhanced patch cord according to thepresent invention;

FIG. 4 is a cross-sectional view showing a conductor and lossy conductorinsulation. according to one embodiment of the present invention;

FIG. 5 is a cross-sectional view of stranded wires having a lossyconductive coating;

FIG. 6 is a detail view of the detail “A” of FIG. 5;

FIGS. 7 a and 7 b are cross-sectional views showing the comparison oftwo cable pairs, with the cable pair of FIG. 7 b having increaseddistance between crosstalk pairs;

FIG. 8 is a cross-sectional view of a cable having a surrounding shield;

FIG. 9 is a cross-sectional view of a cable having a modifiedsurrounding shield;

FIG. 10 is a cross-sectional view of a cable having shieldingsurrounding each wire pair;

FIG. 11 is a cross-sectional view of a cable having a conductive spline;

FIG. 12 is a diagram illustrating varying cable lays along the length ofa cable.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Turning now to FIG. 1, a communication system 10 is shown. In thecommunication system 10, a network device such as the 10 Gb/s Ethernetswitch 12 is connected to a plurality of devices, such as personalcomputers (“PCs”) 14 and 16 by first and second communication cables 18and 20, respectively. It is to be understood that while FIG. 1 shows thecommunication cables 18 and 20 extending from a single network device totwo devices, systems and methods according to the present invention willallow for the suppression of alien crosstalk between communicationcables regardless of the types of devices to which the cables areconnected.

Generally, alien crosstalk resulting from the interaction between thecommunication cables 18 and 20 will be coupled along the entire lengthsof the cables 18 and 20. The cables 18 and 20 act to suppress signaltravelling through them to some degree, such that alien crosstalkoccurring between the cables closer to the Ethernet switch 12 will beattenuated somewhat at the PCs 14 and 16.

Crosstalk suppression is enhanced in the system of FIG. 1 by the use offirst and second enhanced patch cords 22 and 24. The enhanced patchcords 22 and 24 are designed to suppress crosstalk along their lengths,for example by providing additional shielding. In addition, the enhancedpatch cords 22 and 24 attenuate communications signals and noise, suchas crosstalk, travelling through them. Attenuation in the patch cords 22and 24 may be accomplished in a number of ways. For example, attenuationmay be increased by the use of finer-gauge wire within the enhancedpatch cords 22 and 24 or by increasing the number of twists per inch inwires contained within the patch cords 22 and 24.

The strength of alien crosstalk is dependent upon the strength of theinterfering or disturbing signal. Thus, increased attenuation providedby the first enhanced patch cord 22 will reduce the signal level in thefirst communication cable 18. As a result, the alien crosstalk coupledinto the second communication cable 20 from the first communicationcable will be reduced due to attenuation by the first enhanced patchcord 22. Because the alien crosstalk caused by the first communicationcable 18 in the second communication cable 20 will travel in bothdirections in the second communication cable 20, the alien crosstalkwill also be subjected to suppression in the second enhanced patch cord24.

For example, if a signal leaves the Ethernet switch 12 having a signalstrength of 1 volt peak-to-peak, and the first enhanced patch cord 22attenuates to 10% of the initial strength, the signal going from theEthernet switch 12 to the first PC 14 will have a signal strength of 0.1volt peak-to-peak. If 10% of that signal couples as alien crosstalk tothe second communication cable 20, the alien crosstalk in the secondcable will have a signal strength of 0.01 volt peak-to-peak. If thesecond enhanced patch cord 24 also has attenuating properties thatreduce signals to 10% of the initial strength, the alien crosstalk willbe suppressed in the second communication cable 20 to 0.001 voltpeak-to-peak. Thus, the alien crosstalk. has been subjected to theeffects of two enhanced patch cords 22 and 24, and the signal from theEthernet switch 12 through the second communication cable 20 has beensubjected only to the effects of the second enhanced patch cord 24.Optional enhanced patch cords 26 have been shown for connection to thePCs 14 and 16 and similarly operate to reduce alien crosstalk at theuser side of the communication connection.

Enhanced patch cords according to the present invention may beintegrated into a number of connections, as shown by FIG. 2, in which ahorizontal cable plant 28 having multiple cables is enhanced by enhancedpatch cords 30 and 32 provided at first and second ends of thecommunication path.

The enhancement of signal-to-noise ratio using enhanced patch cordsaccording to the present invention is shown in FIG. 3. The dotted lineshows the reduced signal and noise resulting from the enhanced patchcords across the communication frequencies. Because the noise due toalien crosstalk is attenuated to a greater degree than the signal, boththe available bandwidth and the signal-to-noise ratio are improved insystems employing enhanced patch cords according to the presentinvention.

Attenuation may be introduced into patch cords and other communicationcabling using a variety of methods. There are two design parameters toconsider in the design of a lossy patch cord. One parameter is theamount of insertion loss to include in the cable, and the second is theamount of alien crosstalk suppression or susceptibility to have in thecable. Both parameters are preferably addressed in a cable design.

Dielectric loss may be increased as shown in FIG. 4 by providing aconductor 34 within lossy conductor insulation 36 or 38. Dielectric losscan also be increased by using such methods as: (a) cable jacketdielectric lossy material; (b) cable spline dielectric lossy material;and (c) a wire pair shield (which concentrates the E & M field throughthe wire insulation).

The use of a less conductive wire (for example, aluminum wire instead ofcopper wire) will also increase conductor loss. As mentioned above,conductor loss can also be increased by decreasing the conductor wirediameter or increasing the twist per unit length. Increasing the amountof twisting increases the effective length of the cord and henceincreases the conductor loss.

Conductor loss can also be increased by “tinning” a metal wire. Aless-conductive coating on the circumference of the wire will increasethe conductor loss because the current density congregates near thesurface (via the skin effect) and will experience a higher loss throughthe tinned material. The use of stranded wire can also increaseconductor loss, with an increase of loss by roughly 20% for comparablewire gauges. FIG. 5 shows a cross-sectional view of a cable 40 employingtinning and stranded wire. In the embodiment of FIG. 5, stranded copperconductors 42 are provided within a tin skin 44. FIG. 6 is a detail viewof the detail “A” of FIG. 5. The skin is provided at a depth d_(s).

The use of wire with a roughened surface can also increase the conductorloss through the wire.

FIGS. 7 a and 7 b illustrate a technique to decrease the susceptibilityof a cable by increasing the physical distance between crosstalk pairs.First and second cables 46 and 48 are placed in an abuttingrelationship. When the cable jacket material 50 is increased inthickness—for example, to jacket 52, as shown in FIG. 7 b—the distancebetween crosstalk pairs is increased from d₁ shown in FIG. 7 a to d₂shown in FIG. 7 b. According to one embodiment, the cable jacketmaterial 50 is a foamed jacket material. Cable separators may also beused to increase separation between neighboring cables.

Metallic shielding can also be used to reduce susceptibility of aliensignals into a signal cable pair. FIG. 8 is a cross-sectional viewshowing a technique to decrease the susceptibility of a cable by theincorporation of a conductive shield. In FIG. 8, conductive pairs 52 areprovided within an overall conductive shield 54. The conductive shield54, in turn, is provided within a jacket 56. As shown in FIG. 9 (whichincorporates a detail view), in another embodiment a layer of overallshielding 54 may be provided between first and second layers 58 and 60of jacketing material.

FIG. 10 shows another embodiment, in which individual shielding 62surrounds each wire pair.

Another embodiment is shown in FIG. 11, which illustrates the use of aconductive spline 64 or conductive pair separator used to decreasesusceptibility.

In another embodiment, crosstalk may be reduced by modifying the lay ofa cable along its length. The lay of a cable refers to the twisting of acable along its length. In this embodiment, fixed twisted pair lengthsare provided along the length of a cable. Four or more cable lay valuesproviding a four-pair cable with twisted pair lengths over the length ofthe cable meeting the proposed 10 Gb/s Ethernet Near-End Crosstalk(NEXT) requirement are selected. Any four or more cable lay values arechosen at random, with the selection process being described as follows:

1. Cable lays A, B, C, D, . . . ) are selected, with each of the laysmeeting the 10 Gb/s Ethernet NEXT requirement.

2. Any of the four cable lays are selected without replacement duringthe cable lay process.

3. The selected cable lay is provided over a uniform or random length ofcable less than or equal to ten meters.

4. Any of the three or more remaining cable lays are selected andapplied, to the cable construction as described in step 3.

5. The process is repeated until all cable lays have been assigned.

A diagram of a cable length employing random distances between cable laytransitions and using four different cable lays is shown in FIG. 12.

While particular embodiments and applications of the present inventionhave been illustrated and described, it is to be understood that theinvention is not limited to the precise construction and compositionsdisclosed herein and that various modifications, changes, and variationsmay be apparent from the foregoing descriptions without departing fromthe spirit and scope of the invention as defined in the appended claims.

1. A communication cable comprising a plurality of twisted pairs whereinat least one twisted pair of the plurality of twisted pairs has a firstcable lay over a first length of the cable, a second cable lay over asecond length of the cable, and a third cable lay over a third length ofthe cable and further wherein the first, second, and third cable laysare not equal.
 2. The communication cable of claim 1 further comprisinga fourth cable lay over a fourth length of the cable, the fourth cablelay not being equal to the first, second, or third cable lay.
 3. Thecommunication cable of claim 1 wherein the first second and thirdlengths are generally uniform.
 4. The communication cable of claim 3wherein the lengths are equal to ten meters or less.
 5. Thecommunication cable of claim 1 wherein the first second and thirdlengths vary randomly.
 6. The communication cable of claim 5 wherein thelengths are equal to ten meters or less.